1. Field of the Disclosure
The present disclosure relates to a coordinate detecting device, and more particularly, to a coordinate detecting device related to an operation on a screen.
2. Description of the Related Art
In recent years, a device including a coordinate detecting device which specifies a position where a finger touches to operate an electronic apparatus has been actively developed in electronic apparatuses, such as a computer, a mobile phone terminal, and a PDA (Personal Digital Assistant).
For example, as the device that includes the coordinate detecting device, there is a pointing device (coordinate input device), which is called a pad, a touch pad, or a track pad, provided in the computer. The coordinate input device is incorporated into a portable notebook personal computer or is attached to the outside of a desktop computer, and is then used. In this case, it is not necessary to move the coordinate input device, unlike a mouse. Therefore, it is possible to operate the coordinate input device in a limited space, such as on a desk, without any difficulty.
For example, in a portable apparatus, such as a mobile phone terminal or a PDA in which the coordinate detecting device is incorporated into a display screen, the user can directly touch the display screen (operation surface) with the fingers to perform a desired operation.
For example, as the coordinate detecting device, there is a device which uses a variation in capacitance formed between an electrode and a portion around the electrode due to the contact of the finger of the user. In general, a capacitance-type coordinate detecting device includes a plurality of electrodes that are arranged in a matrix in the X-axis direction and the Y-axis direction and a detecting unit that detects a variation in the capacitance of each electrode, and detects the X-axis and Y-axis electrodes with a large capacitance variation among the plurality of electrodes, thereby specifying the position touched by the user.
In addition, in recent years, a coordinate detecting device has been proposed which detects the touch of two fingers at the same time such that the user can perform an intuitive and simple operation and various operations can be performed according to the position or operation of the two fingers. When two fingers touch the operation surface, a large capacitance variation occurs at two points in each of the X-axis direction and the Y-axis direction. Therefore, it is necessary to detect a plurality of points and determine the user's input gesture.
In this case, when the coordinates of the detection target are specified on the basis of a variation in the capacitance of each electrode obtained by scanning a plurality of X-axis electrodes and Y-axis electrodes, a phenomenon (ghosting phenomenon) occurs in which a capacitance variation is detected even in the region which the detection target does not actually touch. In order to solve this problem, JP-A-2010-267093 discloses a method which applies a gradient to the sensor sensitivity to estimate the distance from the input side of a touch location, thereby selecting a touch position.
However, in the method disclosed in JP-A-2010-267093, when the touch position of the detection target is close to the position where the ghosting phenomenon occurs, there is a concern that the detection target cannot be accurately detected. In order to avoid the occurrence of the ghosting phenomenon, a method is considered which detects all of the sensor output values at the intersection points between a plurality of electrodes. However, in this case, it is considered that the number of scanning operations for the electrodes increases significantly and the detection speed of the coordinates of the detection target is reduced.